The clinical use of ultrasound for examination of the fetus has been available for nearly three decades. Because no deleterious effects have been detected in the exposed population, lack of risk has been assumed. However, the existence of subtle effects cannot be precluded. The initial study, "Study of Effects of Ultrasound Radiation of Fetal Gonads," was undertaken to determine if such effects occur in the fetal gonad following in utero exposure to 1 MHz ultrasound. Results of this study showed that adverse effects occurred in the fetal testis subjected to doses of ultrasound which have clinical relevance. These effects have the potential to cause reduced fertility or sterility in the adult animal. It is the purpose of this proposed study to determine the extend of these effects in the adult animal and to assess the role of heat and the resulting stress in the physical mechanism of interaction. To assess effects in the adult, experimental animals will receive in utero ultrasound exposure, be raised to maturity, and the testes subjected to extensive morphometric and histopathological analyses. Findings will be compared to data from sham and cage control specimens. The endpoints analyzed will give specific information regarding the aspect of testicular development which has been altered. The mechanism of heat will be investigated by quantifying histopathological data from testes of fetal mice heated by ultrasonic absorption and heated by a completely different thermal source. The contribution of stress as determined by increased corticosterone concentrations in the dam will also be assessed as imbalance in this hormone in fetal life is known to cause severe reproductive consequences in the adult male. To determine this, quantitative histopathological data from fetuses whose mothers received injections of exogenous corticosterone will be compared to those whose mothers received in utero ultrasound exposure. Experiments will also be carried out to determine the fetal effects of 3.5 MHz focussed ultrasound and if such observed effects are passed on to progeny. The results of this study will provide further understanding of the interaction of ultrasound and the fetal testis as well as provide a basis of risk assessment to the adult who has received in utero ultrasound exposure.